The present disclosure relates generally to a system and method for deploying a downhole casing patch.
Oil and gas wells are ordinarily completed by cementing metallic casing strings in the wellbore. During the drilling, completion and production phase, operators may find it necessary to perform remedial work, repair and maintenance to the casing. For example, the casing is commonly perforated using an explosive charge to evaluate various formations. In addition to the intended perforations, unintentional holes or defects may also be created in the casing. This can allow a leak to develop in the casing permitting the loss of well fluids to a low pressure, porous zone outside the casing, or permit an unwanted formation fluid, such as water, to enter the well. Regardless of the specific application, it is often necessary to deploy a patch to a downhole casing to seal the wellbore from the external formation.
Numerous methods have been developed over the years to deploy patches in casing. One method includes coating a longitudinally corrugated liner with a thin layer of epoxy resin (or other cementing material) and a glass fiber cloth prior to deployment in the wellbore. The coated liner is run into the wellbore (to the damaged area) on a tubing string and then expanded against the casing by forcing an expander device (e.g., a cone) through the liner. While this methodology has been commercially utilized, application of the epoxy resin can be problematic. For example, engagement of the coated liner with the wellbore wall (especially in deviated wells) can cause a loss of the epoxy resin and fiber materials during deployment. Such loss tends to result in an inadequate seal between the patch and the casing. Moreover, the cure cycle of the epoxy begins when mixing is complete. As such, any delay during deployment of the patch can result in premature curing of the epoxy.
Another method includes a metallic tubular that is hydraulically or mechanically expanded into contact with the casing to create a mechanical seal that relies on the contact stress between the expanded tubular and the casing. The metallic tubular is made of a highly compliant material to improve the contact resistance and therefore better seal the damaged section. This tends to require large pressures to expand the tubular and a tubular patch fabricated from an expensive alloy to obtain an effective seal.
Swage style patches are also known in the art and make use of hydraulically or mechanically deformable swages to seal the upper and lower ends of the patch. A conventional threaded tubular patch is deployed between and coupled with the swages. The damaged section is thereby straddled and isolated by the swages and tubular. While swage style patches provide an effective seal, they also tend to create a restriction in the wellbore, since the tubular patch is not expanded.
Epoxy only patches are also known in the art and make use of an epoxy resin that is pumped downhole to the damaged section. After curing, the wellbore is re-drilled to remove any excess epoxy. While such patches are sometimes effective, they rely only on the properties of the epoxy for their strength. As such, the epoxy-only patch is typically ineffective at high pressures.
There remains a need in the art, therefore, for new casing patches and methods for deploying patches in a subterranean cased wellbore.